feat: add setting to keep config synced with a custom URL

[iProdigy]

Closes #487 with a simplified implementation

[iProdigy]

open questions:

• should ::dinkexport include the dynamic config url - probably yes
• should ::dinkimport include the dynamic config url - probably yes
• should there be a chat warning when a user modifies a notifier setting while a dynamic config url is specified (since on next restart, their change may be reverted depending on the contents of the url) - probably not initially worth the complexity

[iProdigy]

looks like there was another request for this

[pajlada]

Works as expected for me, using ::dinkexport all it imported & merged webhook URLs as expected. I did not test if it can override the dynamic config URL

[iProdigy]

i've tested that the dynamic url isn't overwritten :)